Paragonimus pulmonalis (Baelz, 1880) Miyazaki, 1978
ETYMOLOGY: Para = side-by-side and gonimus = gonads along with pulmonalis = for the location in the lung.
SYNONYMS:Distoma pulmonale Baelz, 1883
HISTORY:Paragonimus pulmonalis was resurrected as a separate species by Miyazaki (1978). Miyazaki reported that Paragonimus pulmonalis was a triploid organism that reproduced by parthenogenesis while Paragonimus westermani was diploid and reproduced sexually. Baelz, while he was a professor at the Tokyo Medical School in Japan, first saw the eggs of this parasite in 1880 in patients with pulmonary tuberculosis. Several years later, he realized that he was dealing with a trematode.
GEOGRAPHIC DISTRIBUTION:Paragonimus pulmonalis is found in Japan, Korea, and Taiwan. Miyazaki (1991) believes that Paragonimus pulmonalis is restricted to low lying areas while Paragonimus westermani is found in the mountainous areas of Japan and Taiwan.
LOCATION IN HOST: In cysts in the lungs.
PARASITE IDENTIFICATION: Species of Paragonimus are 7 to 12 mm long, 4 to 8 mm wide, and quite thick, i.e., 4 to 6 mm. For differentiation of the Asian species see Paragonimus westermani.
The eggs have a brown shell, a distinct operculum, and occasionally a knob on the abopercular end; eggs range from 85 to 100 µm in length by 40 to 58 µm in width and tend to be larger on the whole than those of Paragonimus westermani.
LIFE CYCLE: The life cycle of Paragonimus pulmonalis is similar to that of Paragonimus westermani with several marked distinctions. The second intermediate host are the fresh-water crabs Eriocheir japonicus and Eriocheir sinensis, and the fresh-water crayfish Cambaroides similis. Paragonimus pulmonalis adults are parthenogenetic, and they do not, therefore, require a mate within a cyst in order to produce viable offspring. Thus, the tendency to localize in extrapulmonary sites is less than with other Paragonimus spp.
CLINICAL PRESENTATION AND PATHOGENESIS: The signs are similar to those of Paragonimus westermani; the major difference is that these worms are capable of producing eggs when single in cysts. Infection of kittens with single metacercaria produced infections in 14 of 20 animals (Fan and Chiang, 1970). In 11 of the 14 cats that developed infections, the worms matured to egg producing adults; in the remaining 3 animals the flukes remained immature.
TREATMENT: It has not been tried, but it is very likely that praziquantel would be a very successful treatment.
EPIZOOTIOLOGY: Adults of Paragonimus pulmonalis has been reported from the lungs of dogs and cats and as larvae from the muscle of pigs; it has not been found in raccoon dogs or foxes (Miyazaki, 1991). Adults of this parasite have also been recovered from a tiger in Korea.
HAZARD TO OTHER ANIMALS: If mammals ingest the infected crab, there is a possibility that larval flukes will penetrate the intestinal wall and migrate into the abdominal cavity. In permissive hosts, the flukes will go onto develop in the lungs while in some hosts the flukes will persist as in the swine paratenic host. In all these hosts, there is the possibility for associated pathology.
HAZARD TO HUMANS: Many human beings are infected with this parasite; infections are obtained by eating raw or undercooked crabs or meat of the swine paratenic host. Symptoms from the lung lesions can be severe. Similarly, the migration of worms to ectopic locations, such as the brain, can cause severe pathology. Cats are considered a major source of eggs in the environment.
Fan PC, Chiang CH. 1970. Exposure of kittens and puppies to single metacercariae of Paragonimuswestermani from Taiwan. J Parasitol 56:48-54.
Miyazaki I. 1991.. Helminthic Zoonoses. 494 pages. International Medical Foundation of Japan. Fukuoka, Japan.